We report two experiments that investigated whether phonological and/or orthographic shifts in a base word interfere with morphological processing by French 3rd, 4th, and 5th graders and adults (as a control group) along the time course of visual word recognition. In both experiments, prime-target pairs shared four possible relationships: morphological without modification ("nuageux-NUAGE"), morphological with phonological modification ("bergerie-BERGER"), morphological with phonological and orthographic modifications ("soigneux-SOIN"), and orthographic control ("fourmi-FOUR"). In Experiment 1 (60-ms prime duration), priming effects were only significant in the morphological condition without modification in children but in the three morphological conditions in adults. In Experiment 2 (250-ms prime duration) priming effects were significant in all three morphological conditions in each group, independently of form shifts. These results indicate that allomorphic variation does allow for the lexical activation of base words only in the later stages of word recognition in children, whereas this activation is automatic in adults.